Default Child Theme locale is not working in ojs

Hi, I have made a child theme from default one, and i have created a locale/es_ES folder with a locale.po file where I declare my own strings for my theme.

When I declare this variable in the init fuction of my theme:

public function getDisplayName() {
        return __('');

Don’t work.
But if I put this variables in the .po of my parent theme, works. How can i made that my child theme .po file be the one to take this variables??